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Brachiopod associations from late Rhuddanian in South China and their bathymetric significance
HUANG Bing, ZHAN Renbin and WANG Guangxu
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, China
Following the endOrdovician mass extinction, the latest Ordovician and early Silurian was marked by a widespread transgression (Sheehan, 1973, 2001; Brenchley et al., 1994, 2003; Harper and Rong, 1995). The earliest Silurian brachiopod fauna has been described from a number of regions (see Baarli and Harper, 1986; Rong and Zhan, 2006; Cocks and Rong, 2008). However, with rare exceptions (e.g. Rong et al., 2013), the precise age of most assemblages is not sure. Recently, we reported a Dicoelosia (Brachiopoda) population occurred in benthic shelly assemblages of the lower Niuchang Formation from South China (Huang et al., 2013). Constrained by graptolite data, the shelly fauna containing the population was assigned to the recovery interval after the end Ordovician mass extinction (upper Rhuddanian, Llandovery). However, due to the length limitation, we are not talking about the entire brachiopod fauna of this section in this paper. We will simply analyze the taxonomic composition of the brachiopod fauna, and conduct a paleoecological analysis for it including differentiating brachiopoddominated associations and their living environments. The material was collected from the lower Niuchang formation at Xinglongchang section, 1 km southeast of Xinglong Village, southeast of Meitan County Town, northern Guizhou, South China (GPS: 27°4224.6“N, 107°33′02.0”E). The strata are characterized by near shore, shallow water, brownishyellow silty mudstone or grey mudstone that is fossiliferous of several fossil groups, such as brachiopods, trilobites, and a few bryozoans and graptolites.
A preliminary study on the brachiopods (from 9 collections: AGI521522, 524527 and 530532, see Fig. 1) indicates the presence of 6 major groups of brachiopods, including orthids, strophomenids, rhynchonellids, atrypids, athyridids, and spiriferids, represented by 14 genera, amongst which Eostropheodonta, Katastrophomena, Levenea, Dicoelosia, Meifodia? and Eospirifer are the most abundant, and Aegiria, Merciella, Fardenia, Chrustenopora?, Epitomyonia, Zygospiraella, Eospirigerina and Whitfieldella the minorities. Orthids and strophomenids are predominant in both abundance and generic diversity.
Fig. 1. Nine collections made in the lower Niuchang Formation of Meitan County, Guizhou Province, South China. The result of Cluster Analysis for the fossil bed was superimposed and three brachiopod associations were recognized with their water depths proposed.
After browsing specimens bed by bed, a range chart has been made (Fig. 2). From the chart, a trend of decreasing of diversity can be found; and a variation of brachiopods composition is also significant. To know the detail of composition changes, numerical method is needed. Based on binary data of the collections (see Appendix), we made a CA (cluster analysis) for all those collections. Three associations were clearly recognized (Fig. 1): 1) AGI521522, DicoelosiaZygospiraella association; 2) AGI524527 together with AGI530, LeveneaEostropheodonta association; 3) AGI531532, Meifodia?Eospirifer association.
Fig. 2. Range chart showing brachiopod generic composition from AGI521 to AGI 532; the number with “cm” indicates the thickness of the collections.
Dicoelosia population was assigned to BA3 environment with several lines of evidences (Huang et al., 2013). After careful analysis on the DicoelosiaZygospiraella association, the bathymetry of the collections AGI521522 was assigned to “lower BA3” rather than simple “BA3”. The brachiopods younger than the DicoelosiaZygospiraella association, i.e. the LeveneaEostropheodonta association, were thought to live in a shallower environment owing to their sharply decreasing generic diversity (from 10 to 5). Meanwhile, those deeper water indicators, such as Epitomyonia and Dicoelosia, disappeared from the collection AGI 524, which also suggests the water became shallower.
Meifodia?Eospirifer association is the most interesting brachiopod assemblages of all collections, and several similar assemblages of similar age are found in other areas, all of which will be systematically studied in another paper. Its diversity further decreases compared with the association 2. Only 3 brachiopod genera are found, and the association is dominated by Meifodia? and Eospirifer, with only a few specimens of Levenea. Compared with its underlying LeveneaEostropheodonta association, it has much higher abundance and lower diversity, indicating a shallow environment corresponding to BA2.
Is this contradicted to the global transgression? The regional environment should be emphasized to answer this question. The locality of the Xinglongchang section in Meitan County yielding those fossils is paleogeologically located in the northern marginal belt of the Qianzhong (Central Guizhou) Old Land, southern Upper Yangtze Region. Although the beginning of Silurian was marked by a significant and rapid rise of sea level worldwide, in northern Guizhou, the Qianzhong Uplift was still progressing during the Rhuddanian (Chen et al., 2001; Rong et al., 2011). The global sea level drop together with the Qianzhong Uplift at the end Ordovician excised the youngest Ordovician rocks in northern Guizhou, South China. Consequently, the near shore shelly fauna inhabited this area in the southern marginal area of the Upper Yangtze Epicontinental Sea first during the Rhuddanian transgression. The Xinglongchang section is very close to the paleoshoreline, indicating a relatively shallow water environment.
The “seesaw battle” between the global transgression and the Qianzhong Uplift helped sustain a stable regional environment, probably the Qianzhong Uplift get the upper hand during the recovery interval of the end Ordovician mass extinction, which made the shallower trend found in this section. Such situation provided a shallow water habitat to favor the recovery of brachiopods in South China.
References
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Harper, D.A.T. and Rong Jiayu. 1995. Patterns of change in the brachiopod faunas through the OrdovicianSilurian interface. Modern Geology, 20, 83100.
Huang Bing, Rong Jiayu and Harper, D.A.T. 2013. A New Survivor Species of Dicoelosia (Brachiopoda) from Rhuddanian (Silurian) ShallowerWater Biofacies in South China. Journal of Paleontology, 87, 232242.
Rong Jiayu, Chen Xu, Wang Yi, Zhan Renbin, Liu Jianbo, Huang Bing, Tang Peng, Wu Rongchang and Wang Guangxu. 2011. Northward expansion of central Guizhou Oldland through the Ordovician and Silurian transition: evidence and implications. Scientia Sinica Terrae, 41, 14071415.
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Appendix. Binary data of the nine fossil beds for cluster analysis.
AGI
532AGI
531AGI
530AGI
527AGI
526AGI
525AGI
524AGI
522
AGI
521
Katastrophomena000000001
Eostropheodonta001111100
Merciella000000001
Aegiria000000010
Fardenia000000100
Levenea101111111
Dicoelosia000000011
Epitomyonia000000011
Chrustenopora000000010
Zygospiraella000100011
Eospirigerina000000001
Meifodia?111100000
Whitfieldella000000001
Eospirifer110000000
CONOP—A quantitative stratigraphic software and an approach to its parallelization
HOU Xudong1 and FAN Junxuan2
1Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology (NIGP), Chinese Academy of Sciences (CAS), Nanjing 210008, China
2State Key Laboratory of Palaeobiology and Stratigraphy, NIGP, CAS, Nanjing 210008, China
The fossil record preserves a wide range of events that might be used to buildup timescales and to correlate strata from place to place. The events include the originations and extinctions of species (or the FADs and LADs of species), the occurrences of distinctive faunal assemblages, magnetic field reversals, changes in ocean chemistry, and volcanic ash falls (Sadler, 2004). A fundamental task of stratigraphy which involves a large amount of data collection and computation is to determine the regional or global sequence of all these events. It can hardly be achieved only by manual methods if without the help of modern database and computer technology. Quantitative stratigraphic software which is based on recent computing technology and numerical algorithm, can automatically sort, space and calibrate thousands of event data that are collected from hundreds of sections. Thus, this kind of software makes the reconstruction of highresolution timescale possible. Presently, the major quantitative stratigraphic software includes SinoCor (Fan et al., 2013), CONOP (Sadler et al., 2003; Sadler, 2004), HA (Sheets et al., 2012) and so on.
CONOP (Constrained Optimization) is a piece of software which improves the algorithm of graphic correlation. It can correlate all sections from multidimensional space by the simulated annealing algorithm which can find the global or local optimal solution of this kind of problem. But as the amount of data increases, the elapsed time of calculation will rise amazingly. For a normalsize data set which contains 500 sections and 10000 events, it will take as long as several months to compute the data set in CONOP, which is unacceptable for an ordinary research. Thereby, a significant improvement in the computation power of the CONOP software is necessary.
With the rapid development of computer hardware, multicore computers are becoming more and more popular. This kind of computers possess the capacity of parallel computing, therefore, to implement the parallelization of CONOP will be evidently practical that can greatly improve the processing efficiency of CONOP. Parallel computing is a form of computation in which many calculations are performed simultaneously, operating on the principle that large problems can often be divided into smaller ones, which are then solved concurrently. Thus, parallelized CONOP can achieve much more powerful calculated performance.
To achieve much higher computing performance, we parallelize CONOP through three steps. First, we adopted C# which is a programming language developed by Microsoft to rewrite the core code of CONOP9 which was originally written by Fortran. This new version is named as CONOP.net ver. 1.0. Then, several different data sets are carried out by both original Fortran version and new C# version to ensure all the results are the same. Secondly, we observe the time consuming of each function and find out the most timeconsuming functions which should be parallelized (Fig. 1). The “NEWPEN” function is used to calculate penalties of a new possible solution by summed up “RESCTPEN” value of each section. According to the parallel computing rules, the “NEWPEN” function can be parallelized by calculating the “RESCTPEN” function concurrently. Thirdly, we used. NET 4 parallel extensions to implement the parallelization of “NEWPEN” function on the basis of CONOP.net, the C# version of CONOP. As a result, the parallelized CONOP is averagely five times faster than the Fortran version of CONOP while carried out the same size data set (Fig. 2).
Fig. 1. Time costs of top three timeconsuming functions in CONOP. Two diferent sizes of data sets are used for comparison. “ANNEAL”, “NEWPEN” and “RESCTPEN” are the functions in the CONOPs source code. “RESCTPEN” is called by “NEWPEN” and “NEWPEN” is called by “ANNEAL”. According to the chart, with the growth of data sets size, the time costs of the three functions increase significantly.
Fig. 2. Time costs of the three versions of CONOP which carried out a same dataset (including 195 sections and 2730 bioevents). All the tests are carried out on a 3.4 GHz quadcoreequipped PC.
Acknowledgements
This study was supported by National Natural Science Foundation of China (41221001, 41290260, 41272042 and 41202004). This paper is a contribution to the Geobiodiversity Database project (www.geobiodiversity.com) and the IGCP Project 591 “Early to Middle Paleozoic Revolution”.
References
Fan Junxuan, Chen Qing, Melchin, M.J., Sheets, H.D., Chen Zhongyang, Zhang Linna and Hou Xudong. 2013. Quantitative stratigraphy of the Wufeng and Lungmachi black shales and graptolite evolution during and after the Late Ordovician mass extinction. Palaeogeography, Palaeoclimatology, Palaeoecology, 389, 96114.
Sheets, H.D., Mitchell, C.E., Izard, Z.T., Wills, J.M., Melchin, M.J. and Holmden, C. 2012. Horizon annealing: a collectionbased approach to automated sequencing of the fossil record. Lethaia, DOI: 10.1111\/j.15023931.2012.00312.x
Sadler, P.M., Kemple, W.G. and Kooser, M.A. 2003. Contents of the compact disk—CONOP9 programs for solving the stratigraphic correlation and seriation problems as constrained optimization. In: Harries, P.J. (ed.), High resolution approaches in stratigraphic paleontology. Topics in Geobiology, 21, 461465. Dordrecht, Kluwer Academic Publishers.
Sadler, P.M. 2004. Quantitative biostratigraphy—achieving finer resolution in global correlation. Annual Review of Earth and Planetary Sciences, 32, 187213.
Conodont biostratigraphy of the Darriwilian and the Sandbian from Wuhai area, Inner Mongolia, China
JING Xiuchun1,2, ZHOU Hongrui1 and WANG Xunlian1,2
1School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China
2State Key Laboratory of Geobiology and Environmental Geology, China University of Geosciences, Beijing 100083, China
Wuhai, located in the Ordos Basin of northcentral China (Fig. 1), was in the marginal and deep part of the North China Platform during the Ordovician. The Ordovician strata of Wuhai area is biostratigraphically important because of the richness of its macrofaunas and microfaunas. It represents a thick and continuous sequence of the western Ordovician paleoslope of North China Platform.
Fig. 1. AB, Location map of Wuhai. C, Location map of the sampled sections.
Ordovician conodonts from the Wuhai area have been studied for more than 30 years. They were first reported by An et al. (1983) who described some species from the Sandaokan Formation to the Lashizhong Formation. They also roughly correlated the Ordovician successions between Wuhai and North China Platform (An et al., 1983, table 13). Almost in the meantime, Wang and Luo (1984) documented the Ordovician conodonts of this area in a great detail, and recognized five conodont biozones and an assemblage from the Zhuozishan Formation to the Sheshan Formation. Subsequently, An and Zhen (1990) studied the Ordovician conodonts of Wuhai comprehensively. They listed the occurrences of conodonts layer by layer (An and Zhen, 1990, p. 2939), but did not recognize any biozones for this important deepwater conodont fauna. Moreover, the Ordovician conodonts from Wuhai were also reported briefly in several other publications (e.g. Chen et al., 1984; Feng et al., 1998; Wang et al., 2013a, b). All of these works during the past three decades have greatly improved our knowledge on the Ordovician conodonts in Wuhai. However, most of these publications were based on mophological taxonomy and in Chinese. Further revision on these conodonts are necessary in terms of modern multielement taxonomy, and also true to the biostratigraphy of this area in North China.
A total of 28 samples were collected from the Wolonggong Section and the Hatuke Creek Section (Fig. 1). All samples, weighed 2.5 kg on average, were treated with acid and heavy liquid to sort out the conodonts. Many wellpreserved conodonts spanning the middle Darriwilian to the lower Sandbian have been obtain. Some samples are very rich in conodonts. Thirtyeight species of 24 genera occur in most samples and are systematically studied. Having a color alteration index (CAI) of 12, the conodonts show very little, if any, evidence of having been heated.
Five conodont biozones, the Phragmodus polonicus zone, the Dzikodus tablepointensis zone, the Eoplacognathus suecicus zone, the Pygodus serra zone, and the P. anserinus zone, and three subzones, the Pygodus lunnensis subzone, the P. anitae subzone, and the Yantzeplacognathus foliaceus subzone, are recognized. Because of its oceanmargin habitat, the Darriwilian to Sandbian conodont fauna in Wuhai differs from the faunas of North China Platform that typify the shallower and warmer water environments, but is similar to those in South China, Tarim, Atlantic Faunal Region and the marginal area of North America. Simultaneously, Wuhai shares several taxa with North China Platform, that constitutes an effective link in the biostratigraphical correlations (Table 1).
Table 1. Correlation of Ordovician conodont zones of the Wuhai area with those of Baltoscandia and South China
GLOBAL
STAGEBALTOSCANDIA
(Zhang 1998, Lfgren 2004
Bergstrm 2007)SOUTH CHINA（Zhang 1998）WUHAI(This study)
Sandbian
Darriwilain
P. anserinus
A. inaequalis
S. kielcensis
P.serra
E. lindstroemi
E. robustus
E. reclinatus
Y. foliaceus
E. sueciucs
P. anitae
P. lunnensis
E. pseudoplanus
M. ozarkodella
M. hagetiana
Y. crassus
Y. jianyeensisP. anserinus
E. protoramosus
Y. foliaceus
E. suecicus
D. tablepointensis
M. ozarkodella
M. hagetiana
Y. crassus
P. anserinus
P. serra
Y. foliaceus
E. suecicus
P. anitae
P. lunnensis
D. tablepointensis
P. polonicus
References
An Taixiang, Zhang Fang, Xiang Weida, Zhang Youqiu, Xu Wenhao, Zhang Huijuan, Jiang Debiao, Yang Changsheng, Lin Liandi, Cui Zhantang and Yang Xinchang. 1983. The Conodonts of North China and of the Adjacent Regions. Beijing, Science Press. 233 pp.(in Chinese)
An Taixiang and Zhen Zhaochang. 1990. The Conodonts of the Marginal Areas around the Ordos Basin, North China. Beijing, Science Press. 199 pp.
Bergstrm, S. 2007. The Ordovician conodont biostratigraphy in the Siljan region, southcentral Sweden: a brief review of an international reference standard. 9th meeting of the working group on Ordovician Geology of Baltoscandia, Field Guide And Abstracts. Sveriges geologiska underskning, Rapporter och meddelanden, 128, 2641.
Chen Junyuan, Zhou Zhiyi, Lin Yaokun, Yang Xuechang, Zou Xiping, Wang Zhihao, Luo Kunquan, Yao Baoqi and Shen Hou. 1984. Ordovician Biostratigraphy of Western Ordos. Bulletin of Nanjing Institute of Geology and Palaeontology, Academica Sinica, 20, 131.
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Wang Zhihao, Bergstrm, S.M., Zhen Yongyi, Chen Xu and Zhang Yuandong. 2013a. On the integration of Ordovician conodont and graptolite biostratigraphy: new examples from Gansu and Inner Mongolia in China. Alcheringa, 37(4), 510528.
Wang Zhihao, Bergstrm, S.M., Zhen Yongyi, Zhang Yuandong, Wu Rongchang and Chen Qing. 2013b. Ordovician conodonts from Dashimen, Wuhai in Inner Mongolia and the significance of the discovery of the Histiodella fauna. Acta Micropalaeontologica Sinica, 30(4), 323343.
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New data on the paleobiogeography of Cambrian trilobites from
western and northern margins of the Siberian Platform
Igor V. KOROVNIKOV
Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, Novosibirsk, Academician Koptjug avenue 3, Russia
Siberian platform is a unique place for studying the Cambrian biota, including trilobites. Cambrian rocks distribute throughout the platform. Trilobite fossils are numerous and varied. Cambrian trilobites and rocks have been studied by many specialists. To date, more than 1000 species of trilobites have been systematically described from the Cambrian of the Siberian platform, which have been used to develop biostratigraphic zonal scales for different facial regions.
In recent years, the new material was obtained from the marginal parts of the platform—including the western (left bank of the Yenisey River) and the northern (Bennett Island). New data from these areas have allowed to clarify and expand paleogeographic distribution of trilobite complexes of the Siberian platform.
Lower Cambrian
On the left bank of the Yenisey River several wells were found to have Cambrian rocks. The Lower Cambrian trilobites were found in wells Lemok1, Tyya1 and Vostok4. In the well Lemok1 at the depth 2804.42805.9 m trilobites Binodaspis paula and Bonnaria sp. (Korovnikov, 2006) are discovered. These trilobites distribute on the Siberian platform mostly within the TurukhanIrkutskOlekma and Anabar Sinsk facial regions of Botomian Stage (Lower Cambrian). The well Tyya1 yields Bulaiaspis sp. (Kashtanov et al., 1995) which distributes on the Siberian Platform within the TurukhanIrkutskOlekma region in the upper part of the Atdabanian Stage and the lower part of the Botomian Stage. In well Vostok1 the trilobites were found at several levels (Kontorovich et al., 2008). The earliest trilobites Bulaispis cf. sajanica were found at a depth of 3864.6 m. Tungusella manitsa trilobites were discovered at the depth of 3852.3 m. And at the depth of 3831 m, trilobites of Micmaccopsis sp., Bathyuriscellus sp., Astenaspis cf. tenius, Binodaspis sp., Termierella sp. were identified These trilobites are also typical of Botomian Stage in the TurukhanskIrkutskOlekma facial region.
Thus, the trilobite complexes existed in the middle Early Cambrian in western part of the platform had a wider distribution, which is further confirmed by the findings of trilobites in the wells located on the left bank of the Yenisei River.
Lower Cambrian trilobites on Bennett Island were found in the upper part of the shalesandstone formation, which is the lowest at the Cambrian section of the Island. Trilobites identifiable to Judomia and Delgadella and morphologically similar to Fallotaspidella were defined from this part of the section (Danukalova et al., 2014). Representatives of the first two genera are typical of the transitional layers between Atdabanian and Botomian stages in the AnabarSinsk and YudomaOlenek facial regions of the Siberian platform. Higher in the section occur representatives of Lermontovia ex gr. grandis, Neopagetina sp., Anabaraspis splendens, Paramicmacca submissa and some unidentifiable remains of protolenid trilobites. These trilobites are typical of the Toyonian Stage in the AnabarSinsk and YudomaOlenek facial regions. The question of ownership of the Bennett Island to the Siberian platform now disputable. But the presence of Siberian trilobites shows that in Early Cambrian this territory was not far away from the platform and between them there was no significant barriers hindering the distribution of trilobites.
Middle Cambrian
Middle Cambrian trilobites werediscovered in wells Vostok1 and Vostok4. Earlier findings of those Middle Cambrian trilobites Pseudonomocarina sp., Chondranomocare sp., Acontheus sp., Peronopsis ex gr. fallax were from the well Eloguyskaya1, indicating one of the first uncovered Cambrian in this area (Dragunov et al., 1967). In well Vostok1 between the interval 49244871 m trilobites identifiable to Tomagnostus sibiricus, Ptychagnostus contortus, and Triplagnostus gibbus were discovered, which are typical of the upper Amgan Stage. These trilobites were found in the Paydugina Formation characterized by a high content of organic matter and having similar lithology with the Kuonamka Formation on eastern Siberian platform. Trilobites in the well Vostok4 were discovered at depth 3352.5—3352.3 m. Here were found Deltocephalus sp. (Korovnikov et al., 2010), which are typical from the lower Amgan Stage to the lower Mayan Stage of the Middle Cambrian. Trilobites of Pseudanomocarina were found at depth 3101.6—3102.4 m. Species of this genus are distributed in the Siberian platform from the upper Amgan Stage to the lower Mayan Stage of the Middle Cambrian.
Thus, complexes of trilobites that existed in the upper Amgan and the lower Mayan stages in western part of the platform were similar to the trilobite complexes existed at the same time in the eastern part of the Siberian platform.
In the Middle Cambrian part of the section on the Bennett Island numerous and various trilobites of Paradoxides have been discovered. Besides, Ctenocephalus probus, Solenopleura sp., Peronopsis aff. fallax, Acadognostus acadicus, Pentagnostus praeccurens, Pseudanomocarina horrida, and some others are also found (Danukalova et al., 2014). These trilobites are typical of upper Amgan Stage and lower Mayan Stage of the Siberian platform. In the upper part of the section, numerous trilobites identifiable to Agraulos cf. acuminatus, Ciceragnostus citea, Pseudophalacroma crebra, Solenopleura lecta, Anomocarina siberica, Dolichagnostus admirabilis, Anomocare excavatum, Anomocarina siberica, Anomocarina splendens, Clavagnostus repandus, Linguagnostus sibiricus, Pseudagnostus sp., Corynexochus cf. perforatus, Anomocarioides limbataeformis, and Peronopsis sp. (Danukalova et al., 2014) were found, which are typical of upper Mayan Stage. Trilobite complexes of Mayan age on the Bennett Island have many similar forms to those existed contemporaneously in the northeastern Siberian platform and, apparently, were part of a single paleobigeographical province.
Upper Cambrian
In the left bank of the Yenisey River, Upper Cambrian trilobites were found only in the well Vostok1 (Kontorovich et al., 2008) from the Kondes Formation. Such formation yields trilobites of the Nganasan and Tavga Horizons (Late Cambrian), which permit its correlation with the Ayusokkanian Stage and the lower Sakian Stage (Upper Cambrian). Trilobites Kuraspis obscura, Kuraspis similis, Kuraspis spinata, Kuraspis similis ex gr. vera, Kuraspis similis ex gr. deflexa, and Letniites sp. are from the interval 3659—3759 m of the well. And the assemblage corresponds to the Tavga Horizon of the Ayusokkanian Stage (Upper Cambrian). Trilobites Bolaspidina insignis, Parakoldinia sp., and Kuraspis similis from the interval 3902.6—3953.5 m are correlatvie to the Ayusokkanian Stage (Upper Cambrian). Trilobites of the Madui and Entsy Horizons (Late Cambrian) are found higher in the Shedega Formation, permitting a correlation with the upper Sakian Stage (Upper Cambrian). The interval 3241—3400 m contains trilobites (Parakoldinia salairica, Pseudagnostus sp., Parakoldinia striata, Koldinia pusilla, Komaspidella rara, Hadragnostus sp., Homagnostus sp., Bolaspidellus sp., Parakoldinia kureiskaya, Plethopeltoides lepidus, Amorphella sp., and Pesaiella sp.) and brachiopods (Billingsella sp., Eoorthis sp., and Lingulella sp.). Such assemblage is typical of Entsy Horizon of the Sakian Stage (Upper Cambrian).
Trilobites Parakoldinia salairica, Pseudagnostus sp., Parakoldinia striata, Koldinia pusilla, Komaspidella rara, Hadragnostus sp., Homagnostus sp., Bolaspidellus sp., Parakoldinia kureiskaya, Plethopeltoides lepidus, Amorphella sp., Pesaiella sp. and brachiopods Billingsella sp., Eoorthis sp., Lingulella sp. were obtained from the interval 3241—3400 m. This complex is typical of the Entsy Horizon of the Sakian Stage (Upper Cambrian).
The interval 3465—3471 m contains the following trilobites: Idahoia cf. composita, Raashellina paula, Bolaspidina sp., Pesaiella sp., Saonella cf. saonica, Ammagnostus simplexiformis, Bolaspidina cf. insignis, Schoriecare sp., Parakoldinia sp., Komaspidella rara, Nordia aff. lepida, Verkholenoides sp., and Parakoldinia striata, all of which are typical of the Madui Horizon of the Sakian Stage (Upper Cambrian). Higher in the section in the Pyzhina formation were found rare Monosulcatina laeve (depth 2772 m), which is typical of the Ketyi Horizon of the Aksaian Stage (Upper Cambrian).
Trilobites of the Tavga Horizon of the Ayusokkanian Stage are represented mainly by Kuraspis. Records of this genus are widespread in Siberian Platform. They are found in northwestern and southeastern Siberian Platform in the AltaySayan and some other areas. Probably, the territory where the well Vostok1 is located was part of a single paleobiogeographic province within the western Siberian Platform.
Trilobites of the Madui and Entsy horizons of the Sakian Stage have many common constituents with the complexes from the Igarka district (northwestern Siberian platform). Probably, at that time both the territory where the well Vostok1 is located and the Igarka district were part of a single paleobiogeographic province.
Trilobites Gliptagnostus reticulatus, Eugonocare cylindrata, Parabolinites aff. rectus, Oidalagnostus sp., Linguagnostus kjerulfi, Acrocephalella granulosa, Homagnostus sp., Agnostus pisiformis, Pseudagnostus idalis, Pseudagnostus idalis, Plicatolina angusta, Parabolinites rectus, Erixanium sentum, and Eurudagnostus brevispinus were discovered in the upper Cambrian section on the Bennett Island within black shale strata (Danukalova et al., 2014). Among the trilobite species, many are widely spread, and quite a few are prevalent in the northeastern Siberian Platform (Lazarenko, 1966; The Cambrian System of the Siberian Platform, 2008). Thus, in the Late Cambrian, the territory of the Bennett Island continued to maintain close communication with the northeastern Siberian Platform.
The new data show that the Siberian Cambrian trilobite communities were distributed in the western and northern margins of the Siberian Platform: the left bank of the Yenisei River and within the Bennett Island.
References
Danukalova, M.K., Kuzmichev, A.B. and Korovnikov, I.V. in press. Cambrian of the Bennett Island. Journal of Statigraphy and Geological correlation (in Russian).
Dragunov, V.I., Smirnov, A.L. and Chernysheva, N.E. 1967. Lower Paleozoic sediments in the basement of the eastern West Siberian Plain (Eloguiskaya wells). Dokl. AN SSSR, 172(2), 420422.
Kashtanov, V.A., Varlamov, A.I. and Danilova, V.P. 1995. Paleozoic Sediments on the Left Bank of the Yenisei River (Tyiskaya Parametric Well): Geologic Structure and Petroleum Potential. Preprint of the United Institution of Geology and Geophysics, and Mineral, Novosibirsk, No. 1.
Kontorovich, A.E., Varlamov, A.I., Emeshev, V.G., Efimov, A.S., Klets, A.G., Komarov, A.V., Kontorovich, V.A., Korovnikov, I.V., Saraev, S.V., Filippov, Yu.F., Varaksina, I.V., Glinskikh, V.N., Luchinina, V.A., Novozhilova, N.V., Pegel, T.V., Sennikov, N.V. and Timokhin, A.V. 2008. New type of Cambrian section in eastern part of West Siberian Plate (based on Vostok1 stratigraphic well data). Russian Geology and Geophysics (Geologiya i Geofizika), 49(11), 843850 (11191128).
Korovnikov, I.V. 2006. New trilobites finds from Lower Cambrian deposits of the Yenisey River left bank (based on data from boring of Lemok1 well). News of paleontology and stratigraphy. Supp. Russian Geology and Geophysics Journal, 8, 914.
Korovnikov, I.V., Terleev, A.A., Postnikov, A.A., Saraev, S.V., Karlova, G.A., Nagovitsin, K.E., Tokarev, D.A., Popov, N.V., Luchinina, V.A. and Novozhilova, N.V. 2010. New paleontological data on the Cambrian units of the CisYenisei part of the West Siberian megabasin (from drilling data on the Vostok4 parametric well, Krasnoyarsk Territory). 2729, 9196. In: Proceedings of II AllRussian Conference with International Participation “The Basement and Framing of the MesoCenozoic West Siberian Basin, Their Geodynamic Evolution and Petroleum Potential”. Tyumen, Geology, Novosibirsk (in Russian).
Lazarenko, N.P. 1966. Biostratigraphy and some new trilobites of Upper Cambrian of the Olenek Uplift and Kharaulakh mountains. Memoir of Paleontology and Biostratigraphy, 11, 3378 (in Russian).
The Cambrian system of the Siberian Platform. 2008. Part 2: NorthEast of the Siberian platform. MoscowNovosibirsk, PIN RAS. 139 pp.
Ontogeny and larval ecology of paradoxidid trilobites
(Eccaparadoxides and Hydrocephalus) from the SkryjeTrˇovice
Basin (Czech Republic)
Luka＇sˇ LAIBL1, Oldrˇich FATKA1, Jorge ESTEVE2 and Petr BUDIL3
1Charles University, Faculty of Science, Institute of Geology and Palaeontology, Albertov 6, 128 43 Prague 2, Czech Republic
2University of West Bohemia, Center of Biology, Geosciences and Environment, Klatovsk, 51, 306 14 Pilsen, Czech Republic
3Czech Geological Survey, Klrov 3, Praha 1, 118 21, Czech Republic
Fig. 1. Location of the SkryjeTrˇovice Basin in the Bohemian Massif (A), geographic (B) and stratigraphic (C) distribution of the localities.
Several outcrops within the SkryjeTrˇovice Basin (Fig. 1) yielded a diverse assemblage of protaspid and meraspid stages of various trilobites, stratigraphically belonging to Cambrian Series 3 (Fatka, 2004; Laibl et al., 2014; Geyer et al., 2008). In this contribution we focused on the ontogeny of two species of the family Paradoxididae Hawle and Corda, 1847, namely Eccaparadoxides pusillus (Barrande, 1846) and Hydrocephalus carens Barrande, 1846. Although ontogeny of these two taxa was studied by earlier authors (e.g. Pompeckj, 1896; Raymond, 1914; Raw, 1925; uf, 1926; Ricˇka, 1943; najdr, 1958) most of these studies focussed on morphological description only. Exceptional preservation and abundance of early ontogenetic stages of the above mentioned species, however, allows detailed quantitative study and discussion on functional morphology, ecology, distribution and possible phylogenetic relationships.
The protaspid and early meraspid stages of E. pusillus are characterised by elliptical, slightly vaulted glabella with one sagittal and four pairs of lateral glabellar furrows (Fig. 2B). On the other hand the early stages of H. carens have large, inflated and subcircular glabella with one short sagittal furrow developed in its posterior part (Fig. 2A). Both taxa have quite long intergenal spines and also macrospines on the first and the second trunk segments. Comparison of the corresponding stages of the E. pusillus and H. carens shows a significant difference in size. Whereas the earliest known stage of Eccaparadoxides reaches approximately one millimeter in diameter, the earliest stage of Hydrocephalus is almost twice larger. According to globular morphology, combined with significant oblique directed spines we suggest that at least the first protaspid stages were most likely planktonic in both taxa. The extraordinary large dimension in the protaspides of H. carens may be indication of a lecitotrophy.
Fig. 2. Dorsal morphology of protaspid stages of Hydrocephalus carens (A) and Eccaparadoxides pusillus (B). Scale bars = 1 mm.
Variability in paradoxidid protaspides may be valuable for understanding of phylogenetic relationships within the family Paradoxididae.Both Hydrocephalus and Eccaparadoxides share highly advanced protaspid morphology compare to Paradoxides (cf. Westergrd, 1936). The latter genus share many characters with early ontogenetic stages of the superfamily Redlichioidea Poulsen, 1927 (e.g. rather narrow glabella with distinct sagittal furrow, see Dai and Zhang, 2012) and thus represent most likely the plesiomorphic state.
Acknowledgements
This research is supported by GA UK (Grant Agency of Charles University) No. 656912: Ontogeny of selected taxa of trilobites and agnostids from the Middle Cambrian of the Barrandian area and by the Czech Geological Survey project No. 334600, respectively.
References
Barrande, J. 1846.Notice préliminaire sur le Systême silurien et les Trilobites de Bohême. Hirschfeld, Leipzig. 97 pp.
Dai Tao and Zhang Xingliang. 2012. Ontogeny of the redlichiid trilobite Metaredlichia cylindrica from the Lower Cambrian (Stage 3) of South China. Journal of Paleontology, 86(4), 646651.
Fatka, O. 2004. Association of fossils and history of research at the Trˇovice, Pod hrukou locality (Middle Cambrian, SkryjeTrˇovice Basin, Barrandian area).Journal of the Czech Geological Society, 49(34), 107117.
Geyer, G., Elicki, O., Fatka, O.and Zylinska, A. 2008. Cambrian. 155202. In: McCann, T. (ed.), Geology of Central Europe, Geological Society of London.
Hawle, I.and Corda, A.J.C. 1847. Prodrom einer Monographie der bhmischen Trilobiten. J.G. Calve, Prague. 176 pp. [Reprinted in 1848 in Abhandlungen der kniglichen bhmischen Gesellschaft der Wissenschaften, 5(5), 119292.]
Laibl, L., Fatka, O., Crnier, C.and Budil, P. 2014. Early ontogeny of the Cambrian trilobite Sao hirsuta from the SkryjeTrˇovice Basin, Barrandian area, Czech Republic. Bulletin of Geosciences, 89(2), 293309.
Pompeckj, F. 1896. Die Fauna des Kambriums von Tejovic und Skrej in Bhmen.Jahrbuch der kaiserlichkniglichen geologischen Reichanstalt, 45, 495615.
Poulsen, C. 1927. The Cambrian, Ozarkian, and Canadian faunas of northwest Greenland.Meddelelser om Grnland, 70, 233343.
Raw, F. 1925. The development of Leptoplastus salteri (Calloway) and of other trilobites (Olenidae, Ptychoparidae, Conocoryphidae, Paradoxidae, Phacopidae, and Mesonacidae). Journal of the Geological Society, London, 81, 223324.
Raymond, P.E. 1914. Notes on the Ontogeny of Paradoxides, with the Description of a new Species from Braintree, Massachussets. Bulletin of the Museum of Comparative Zoology, 58(4), 225244.
Ricˇka, R. 1943.Píspěvek k ontogenii cˇeskch Paradoxid a rodu Sao (Beitrag zur Ontogenie der bhmischen Paradoxiden und der Gattung Sao). Věstník Krlovské Cˇeské spolecˇnosti nauk, Tída matematickopírodovedeck, 1943, 143.
najdr, M. 1958. Trilobiti cˇeského stedního kambria (Bohemian Middle Cambrian trilobites). Rozpravy Ｕ＇stedního ústavu geologického, 20, 1280.
uf, J. 1926. O cˇeskych Paradoxidech se zvltním zetelem k jejich vvoji.Sborník Sttního Geologického Ｕ＇stavu Cˇeskoslovenské Republiky, 6, 3167.
Westergrd, A.H. 1936. Paradoxides oelandicus beds of land, with the account of a diamond boring through the Cambrian at Mossberga. Sveriges Geologiska Underskning, C349, 167.
New morphological specificity of vetulicolians and its implications
LI Yujing, ZHAO Jun, CONG Peiyun and HOU Xianguang
Yunnan Key Laboratory for Palaeobiology, Yunnan University, Kunming, 650091, China
Vetulicolians are enigmatic Early Cambrian metazoans with a controversial phylogenetic history. A great number of specimens discovered in Cambrian sediments at many localities in the world reveal that the Vetulicolians take the shape of symmetrical bivalved carapace with structures of lateral pouches and anthropodlike posteroir segments. Eight species of Vetulicolians from the Chengjiang Biota and 2 from the Guanshan Biota, including two classes namely the Vetulicolida and the Banffozoa, were hitherto documented. We carry out a study to compare the Genus Vetulicola between the Chengjiang Biota and the Guanshan Biota. Evidences indicate that a dorsal fin structure functions as a joint connecting the anterior and posterior parts of the Vetulicolians, and from the Chengjiang to the Guanshan Biota, this dorsal fin moved toward the anterior section in trends of evolution. New vetulicolian specimens (discovered from the Lower Cambrian Canglangpu Formation in the Guanshan Biota of Yunnan Province, southwest China) support this morphological inclination. The new vetulicolian Vetulicola kunmingensis sp. nov. shares remarkable features with Vetulicola rectanglata that contains nearly straight anterior edge of anterior body structure in lateral view, whereas blunt posterior edge. Some specimens from the Guanshan Biota also suggest that the anterior body is subrectangular in lateral view. Similarly, these morphological differences in the posterior edge of anterior body occurs in specimens of the Chengjiang Biota. Preliminary observation suggests these original differences are interpreted as sexual dimorphism.
Preliminary report on the chitinozoans from the Lower Ordovician Tungtzu and Hunghuayuan formations of Tongzi, northern Guizhou, southwest China
LIANG Yan, TANG Peng and ZHAN Renbin
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
As an extinct group of organicwalled, planktic microfossils,chitinozoan is characterized by its wide distribution and short temporal range of its species, which enables it to become an important tool in the stratigraphic correlation. In South China, Early Ordovician chitinozoans have been sporadically studied. In order to investigate the early evolution of chitinozoans and their biodiversification during the Early and Middle Ordovician and its dynamics, some case studies have been conducted for this particular time interval on the Yangtze Platform of South China paleoplate.
This paper is to report some preliminary results of the chitinozoans from the Lower Ordovician Tungtzu and Hunghuayuan formations at Honghuayuan of Tongzi County, northern Guizhou Province. Grahn and Geng (1990) reported 2 genera and 5 species of chitinozoans from 3 samples at this section. In this study, we made 12 samples here from which 7 genera and 16 species have been obtained and identified, including some index fossils such as Lagenochitina estonica Eisenack, Euconochitina symmetrica (Taugourdeau and de Jekhowsky), Eremochitina brevis Taugourdeau and de Jekhowsky, Lagenochitina brevicollis Taugourdeau and de Jekhowsky, Lagenochitina obeligis Paris, together with some regional species such as Lagenochitina yilingensis Chen et al., Lagenochitina chongqingensis Chen et al. and also with some widespread constituents such as Conochitina exilis Bockelie and Desmochitina minor Eisenack.
Locality, lithology and samples
The Honghuayuan section (N28°4′31“, E106°51′45”) is about 7 km southeast of Tongzi county town, northern Guizhou, southwest China. The section crops out along a long mountain slope and exposes a quite continuous succession from the Upper Cambrian Loushankuan Group at the foot of the slope to the Lower Silurian Lungmachi Formation on the top. Nowadays, the Cambrian strata and most of the Tungtzu Formation (Tremadoc) have been covered since the highway G75 was constructed. So, only 3 samples were made in the uppermost 12 m of the Tungtzu Formation. On the other side of the highway, five more collections were made from the middle Tungtzu Formation.
The Tungtzu Formation (Tremadoc) at Honghuayuan is 72.3 m thick (Zhan and Jin, 2007), mainly consisting of mediumto thickbedded argillaceous stripped bioclastic limestone interbedded with shales in its lower part and thinto mediumbedded dolomitic limestone and few shales in its middle to upper part. There are 2 m thick shales at the uppermost Tungtzu Formation yielding numerous chitinozoans (sample 13GTH12, more than 2500 individuals were obtained.).
The uppermost Tremadocian to lower Floian Hunghuayuan Formation is characterized by dark grey mediumto thickbedded, weatheringresistant bioclastic limestone with 0.57 m thinbedded bioclastic limestone interbedded with very few layers of shales. Four samples have been made amongst which 2 from the uppermost 0.57 m yielding abundant chitinozoans.
Altogether 12 samples were made at this section on the purpose of chitinozoan study, amongst which 8 from the Tungtzu Formation and 4 from the Hunghuayuan Formation. All samples were prepared in the lab according to the standard palynological procedures (Paris,1981). The weight of each sample is about 50 g.
Preliminary results of chitinozoan study
Among the 12 samples,three are productive: 13GTH12 from the uppermost Tungtzu Formation, AFI 996 and AFI 998 from the Hunghuayuan Formation. One sample (13GTH05) yields only one individual of chitinozoan. And none chitinozoans have been obtained from the other 8 samples after our preliminary preparation. More than 4000 chitinozoans were discovered for this study including 7 genera and 16 species (Fig. 1).
Fig. 1. Preliminary results of chitinozoan stratigraphical range chart from the Tungtzu and Hunghuayuan formations at Honghuayuan, Tongzi, Guizhou Province.
In the middle Tungtzu Formation, one single specimen, similar to E. brevis?, has been recovered from the sample 13GTH05. It has the same vesicle outline and size as E. brevis but differs from the latter in the morphology of copula at its base. Some more rocks are being analysed for this sample in order to get more material.
The samples (e.g. 13GTH12) collected from the uppermost Tungtzu Formation (upper Tremadoc) yield thousands of chitinozoans, such as Euconochitina symmetrica (Taugourdeau and de Jekhowsky), Lagenochitina brevicollis Taugourdeau and de Jekhowsky, Lagenochitina obeligis Paris, Lagenochitina cf. obeligis Paris, Desmochitina minor Eisenack, Bursachitina sp. and Lagenochitina sp. The index fossil E. symmetrica takes a predominant position by taking more than 95% of the total chitinozoans found.
The sample AFI 996 is from the uppermost Hunghuayuan Formation (middle Floian, corresponding to the graptolites Tetragraptus approximatus Biozone), and yields more than 600 individual specimens of chitinozoans. Five genera and 10 species are identified, including Eremochitina brevis Taugourdeau and de Jekhowsky, Conochitina exilis Bockelie, Conochitina decipiens Taugourdeau and de Jekhowsky, Amphorachitina conifundus? Poumot, L. obeligis Paris, L. brevicollis Taugourdeau and de Jekhowsky, Lagenochitina yilingensis Chen et al., Lagenochitina chongqingensis Chen et al., Lagenochitina lata? Taugourdeau and de Jekhowsky, Bursachitina sp., amongst which E. brevis takes the predominant position (more than 65 % of the total), and L. obeligis (about 15%) together with L. yilingensis (about 10 %) the second and third positions respectively. About 0.4 m above this sample, about 350 chitinozoans are obtained from the sample AFI 998, and again E. brevis takes the leading position (about 99% of the total). Only a few others like C. exilis and L. yilingensis together with one broken piece of Desmochitina are associated.
Fig. 2. Some representative chitinozoans from the Tungtzu and Hunghuayuan formations at Honghuayuan section. All scale bars represent 100 μm. (A) Lagenochitina chongqingensis Chen et al., 2009 (Collection AFI 996); (B) Lagenochitina brevicollis Taugourdeau and de Jekhowsky, 1960 (13GTH12); (CE) Euconochitina symmetrica (Taugourdeau and de Jekhowsky, 1960) (all from collection 13GTH12); (F) Desmochitina minor Eisenack, 1931 (13GTH12); (G) Bursachitina sp. (AFI 996); (HI) Eremochitina brevis Taugourdeau and de Jekhowsky, 1960 ( H: AFI 998; I: AFI 996); (J) Eremochitina brevis Taugourdeau and de Jekhowsky, 1960 (13GTH05); (K) Lagenochitina lata Taugourdeau and de Jekhowsky, 1960 (AFI 996); (L) Amphorachitina conifundus Poumot, 1968 (AFI 996); (M) Lagenochitina obeligis Paris, 1981 (13GTH12); (NO) Lagenochitina yilingensis Chen et al., 2009 (AFI 996); (P) Conochitina decipiens Taugourdeau and de Jekhowsky, 1960 (AFI 996); (Q) Conochitina exilis Bockelie, 1980 (AFI 996).
Chitinozoan biostratigraphy
According to our preliminary study,one chitinozoan biozone, the Euconochitina symmetrica Biozone, could be recognized from the uppermost Tungtzu Formation, and one assemblage, the Eremochitina brevis Assemblage, exists in the uppermost Hunghuayuan Formation.
With a wide distribution and a short geological range, E. symmetrica is regarded as the chitinozoan index fossil for the period from late Tremadocian to early Floian of Laurentia (Achab, 1989; Achab et al., 2003), North Gondwana (Paris, 1990) and Yangtze Platform, South China (Wang and Chen, 2003). Wang et al. (2013) moved the E. symmetrica biozone down to the middle to upper Tremadocian, corresponding to the upper part of the graptolite Araneograptus murrayi biozone at Nanba section, South China. Although we have not found any E. symmetrica from the Hunghuayuan Formation at Honghuayuan section, it has been obtained from the Hunghuayuan Formation at Houtan, Xishui County, northern Guizhou, about 72 km northwest of the Honghuayuan section. The material from Houtan is being systematically studied.
Eremochitina brevis is an index fossil for the upper Floian of North Gondwana (Paris, 1990; Cooper and Sadler, 2012) and Alvalonia (Samuelsson and Verniers, 2000). However, at Honghuayuan section, it appears in the lower Floian with massive individual numbers, associated with L. obeligis, L. brevicollis, A. conifundus, L. yilingensis, C. exilis, L. chongqingensis, L. lata? and B. sp. It has also been recovered from the middle Hunghuayuan Formation at Chenjiahe, northern Yichang, western Hubei Province (Zhang and Chen, 2009). Here we use the E. brevis assemblage for the upper Hunghuayuan Formation to distinguish the chitinozoan assemblage from the upper Tungtzu Formation. Further study is required to reveal the relationship between the E. brevis assemblage and the E. symmetrica biozone.
To date, our preliminary study suggests the early chitinozoans from South China had a close relationship with those of north Gondwana.
Conclusions
In this study,7 genera and 16 species of chitinozoans have been recovered from the Tungtzu and Hunghuayuan formations (TremadocFloian, Lower Ordovician), which increase the chitinozoan diversity of this interval. Euconochitina symmetrica Biozone can be correlated with its corresponding biozones of North Gondwana, Laurentia and Yangtze Platform (South China). The preliminary study suggests a close relationship between North Gondwana and South China during the late Tremadocian to early Floian. Further investegations are required for the early chitinozoans of South China to reveal their biostratigraphical significance and macroevolutionary implications.
Acknowledgements
Our sincere thanks go to Liu Jianbo from Peking University and Wang Guangxu from Nanjing Institute of Geology and Palaeontology (NIGP) for their kindest help in the field, to Zhang Yong from NIGP for his help in the lab and to Mao Yongqiang for the SEM photographing. Financial supports are from the National Natural Science Foundation of China (41221001, 41290260, 41172012). This paper is also a contribution to IGCP project 591 “Early to Middle Paleozoic Revolution”.
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Wang Wenhui, Feng Hongzhen, Vandenbroucke, T.R.A., Li Lixia and Verniers, J. 2013. Chitinozoans from the Tremadocian graptolites shales of the Jiangnan Slope in South China. Review of Palaeontology and Palynology, 198, 4561.
Wang Xiaofeng and Chen Xiaohong. 2003. Ordovician chitinozoan diversification evens in China. Science in China (Series D), 33(3), 210215.
Zhang Miao and Chen Xiaohong. 2009. Early Ordovician chitinozoans from the Fengsiang and Hunghuayuan Formations in Chenjiahe of Yichang, Hubei. Journal of Stratigraphy, 33(4), 425431.
Microfacies of the Lower to Middle Ordovician Zitai Formation of southern Anhui and its implications
LUAN Xiaocong1, 2, LIU Jianbo3 and ZHAN Renbin1
1State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
2University of Chinese Academy of Sciences, Beijing 100049, China
3School of Earth and Space Sciences, Peking University, Beijing 100871, China
The Great Ordovician Biodiversification Event (GOBE) is a rapid radiation of marine biodiversity in Ordovician Period, especially during the Early to Middle Ordovician. The most important difference between the Cambrian Explosion and GOBE lies in that the latter was manifested mainly on lower ranks like order, superfamily, genus and species. Conducting case studies in South China for more than ten years, Chinese researchers have already achieved quite a few preliminary results, amongst which some are initiative that attract much attention from international colleagues (e.g. Liu, 2006; Zhou et al., 2006; Zhan et al., 2005, 2006; Zhang et al., 2007, 2010; Yan et al., 2011; Wu et al., 2012). Yangtze Region of South China, especially the middle part of the Upper Yangtze Platform concentrates most of those case studies, while the marginal area of the Platform is less concerned. The Zitai Formation (Floian to Dapingian) is a unique lithologic unit developed along the platform margin in Yangtze Region. Its biofacies is somewhat similar to those of other places on the Yangtze Platform, and also has some apparent uniqueness. To further investigate its sedimentology and the environmental background might be essential to the understanding of GOBE in South China.
The Zitai Formation was named by Mu et al. (1974) at Zitai of Heshui town, Yinjiang County, northeastern Guizhou Province (N28°3′9″, E108°33′57.2″). It is characterized by purple and greyishgreen nodular limestone and argillaceous limestone, correlative with the Dawan Formation and the Meitan Formation that are widely developed in the Yangtze region (Chen et al., 1995; Chen and Zhan, 2006; Dong et al., 1997; Gao et al., 2000; Wang et al., 1996; Zhang et al., 2002). The typical Zitai Formation could be further divided into three parts upwards: (1) Yellowish brown to yellow green with purple red shale; (2) Purple red nodular limestone; (3) Yellowish brown sandstone. Some primitive investigations have already revealed its potential in the study of GOBE (e.g. Wu et al., 2007; Wu and Wang, 2008; Wu et al., 2012; Zhang, 2003). This paper is to report our first try to study the carbonate mircofacies of the Zitai Formation, and the sedimentological background of the biotic diversity change.
Research sections locate in southern Anhui Province, the west part of the Lower Yangtze Platform, representing the eastern end of the Zitai Formation in the Yangtze Region. The Zitai Formation in the study area is thinner than that of the Upper Yangtze Platform, and has a higher carbonate proportion in the rocks. Lithologically it lacks yellowish brown sandstone in its upper part and yields no macroshelly fossils that are common in the Zitai Formation of the Upper Yangtze Platform. And most importantly the Zitai Formation in the study area is almost entirely purple red in color. Two sections are carefully investigated: the Dingxiang section in Shitai County and the Hongjia section in Chizhou City. Careful observation and sampling throughout the Zitai Formation were made, and tens of thin sections were used to study the microfacies of the formation.
The low abundance of grain and low compositional maturity of the Zitai Formation suggest a relatively stable paleoenvironment during the development of the formation, that makes it difficult to differentiate the microfacies for the Zitai Formation. Based on 48 thin sections (17 from the Dingxiang Section, Z002—Z004, Z007—Z020; 31 from the Hongjia Section, 12SC126—12SC120, 12SC300—12SC314), nine carbonate microfacies (MF1—9) are recognized according to the type and proportion of matrix and grain (mainly bioclasts ) and argillaceous soil ratio (Fig. 1).
Fig. 1. The distribution pattern of carbonate microfacies in ramp.
MF1 Calcareous Shale Facies. (1) Characteristics: shale content >50%, commonly identified beddings in the field, easy to be recognized; (2) Suggested environment: middle and lower deep subtidal zone to shaly basin.
MF2 Argillaceous Mudstone Facies. (1) Characteristics: bioclast (the most common type of grain in the rocks) content <10%, medium to high shale content (10%—50%), micritic cementation; (2) Suggested environment: middle and lower deep subtidal zone to upper shaly basin.
MF3 Mudstone Facies. (1) Characteristics: bioclast content <10%, low shale content (<10%), micritic cementation; (2) Suggested environment: middle and lower deep subtidal zone.
MF4 GastropodOstracoda Wackstone Facies. (1) Characteristics: bioclast content 15%—48%, about 35% of them are gastropods and ostracods, uncertain shale content, micritic cementation; (2) Suggested environment: middle and lower deep subtidal zone.
MF5 Calthropbearing Wackstone Facies. (1) Characteristics: bioclast content 22%—23%, about 35% of them are calthrops, medium shale content, micritic cementation; (2) Suggested environment: middle and lower deep subtidal zone.
MF6 Argillaceous Bioclastsbearing Wackstone Facies. (1) Characteristics: bioclast content 10%—23%, medium to high shale content, micritic cementation; (2) Suggested environment: upper middle deep subtidal zone to upper shaly basin.
MF7 Argillaceous Bioclastic Wackstone Facies. (1) Characteristics: bioclast content 25%—48%, medium to high shale content, micritic cementation; (2) Suggested environment: deep subtidal zone.
MF8 Bioclastic Wackstone Facies. (1) Characteristics: bioclast content 33%—48.4%, low shale content, micritic cementation; (2) Suggested environment: lower shallow subtidal zone to upper part of the lower deep subtidal.
MF9 Bioclastic Packstone Facies. (1) Characteristics: bioclast content >50%, low shale content, micritic cementation; (2) Suggested environment: lower shallow subtidal zone to middle deep subtidal.
The results of the detailed microfacies analysis are shown in Figure 2. To improve the research precision, Dunhams wackstone (10%—50% grain) is further divided into grainbearing wackstone (10%—25% grain) and wackstone (25%—50% grain).
Fig. 2. The sealevel change of the Zitai Formation at Dingxiang and Hongjia sections.
According to the observation on thin sections, the matrix of the rocks is found to be all micritic, indicating a very quiet environment for the formation. The grains are basically bioclasts, which include trilobites, echinoderms, gastropods, brachiopods, sponges, ostracods and bryozoans. Trilobites and echinoderms, the most common bioclasts in thin sections, are both benthic animals, which require a high degree of oxygen for them to survive. The trilobite fragments in the thin sections range from 1 cm to hardly recognizable, and are poorly sorted and rounded, and long twisted strip in shape, so they should be autochthonous and were not transported for a long distance. Fragments of echinoids and crinoids range from 1—2 cm to hardly recognizable, and rounded in shape and not apparently sorted. All the other bioclasts show similar characters.
All microfacies indicate to an environment of deep subtidal zone, i.e. the Zitai Formation was deposited in a relatively deep water environment with a high degree of oxgen.
At the Dingxiang section, MF2, MF4, MF6 and MF8 are well developed. Through the change of lithology and bioclast, four transgressions (D1, D2, D3 and D4) have been recognized at this section. The sedimentary environment of the Zitai Formation at Dingxiang is proposed to the middle to lower deep subtidal with a deepening upward trend. At Hongjia section, MF1—9 are all developed and four transgressions (H1, H2, H3 and H4) could be recognized occurred. A similar paleoenvironment, i.e. middle to lower deep subtidal, could be proposed for the Zitai Formation at Hongjia. The biostratigraphic correlation between these two sections is impossible at the moment because the biostratigraphic study at Dingxiang has already finished (Wu, 2011) and is going on at Hongjia. Even so, the fours transgressions recognized at both localities are well correlative (Fig. 2).
There are also some significant differences between the Zitai Formation of two sections. For example, MF1, MF3, MF5, MF7 and MF9 are missing at Dingxiang, while MF2 are most developed. On the contrary, all mircofacies could be recognized at Hongjia, amongst which three of them (MF4, MF8 and MF9) are very welldeveloped. Showing in Figure 1, the water depth of the Zitai Formation at Hongjia might be shallower than that of Dingxiang. Besides, the sealevel change at Hongjia is also more frequent and dramatic than that of the other section.
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Deep thoughts from deep time—central nervous systems of
Cambrian panarthropods
MA Xiaoya1,2, CONG Peiyun1, HOU Xianguang1, Gregory EDGECOMBE2 and
Nicholas STRAUSFELD3
1Yunnan Key Laboratory for Palaeobiology, Yunnan University, Kunming, China
2Department of Earth Sciences, The Natural History Museum, London, UK
3Department of Neurosciences and Center fro Insect Science, University of Arizona, Tucson, USA
Comparative study of nervous systems and sensory organs is fundamental for understanding the evolutionary relationships between major arthropod groups and their ecological adaptation throughout evolutionary history. Exceptionally wellpreserved Cambrian panarthropod fossils provide a rich and underexploited source of data on neural and sensory anatomy during the early stages of the panarthropod radiation. Recent reports of the central nervous systems and visual organs from the Chengjiang arthropods Fuxianhuia protensa and Alalcomenaeus sp. demonstrate that arthropods had acquired complex organ systems by the early Cambrian and the two main configurations of the brain and eyes observed in Mandibulata and Chelicerata had diverged. Cambrian stem lineage arthropods (namely dinocaridids and lobopodians) represent unique transitional phases of arthropod evolution that can shed light on our understanding of the origin and divergence of arthropod central nervous systems and sensory organs. The brain discovered from a new Cambrian anomalocaridid provides direct evidence for the segmental composition of the anomalocaridid head and its appendicular organization. Correspondences in brain organization between anomalocaridids and Onychophora resolve preprotocerebral ganglia, associated with preocular frontal appendages, as characters of the last common ancestor of arthropods and onychophorans.
Insights into the RhuddanianAeronian and AeronianTelychian
boundary intervals from eastern and Arctic Canada
Michael J. MELCHIN1 and KevinDane MACRAE2
1Department of Earth Sciences, St. Francis Xavier University, Antigonish, NS, Canada B2G 2W5
21061 Ospwagon Dr., Thompson, MB, R8N1P8, Canada
Since the base of the Aeronian Stage was formally defined it has been considered to coincide with the globally recognizable base of the Demirastrites triangulatus Zone. Recent studies, however, indicate that the GSSP actually correlates to a level within the D. triangulatus Zone (Davies et al., 2013). At the GSSP the level is biostratigraphically marked only by the first appearance datum (FAD) of Monograptus austerus sequens, a taxon not known to occur outside of northern Europe.
The RhuddanianAeronian and AeronianTelychian successions on Cornwallis Island, Nunavut, were documented by Melchin (1989) and Lukasik and Melchin (1997), but since then significant new information has become available, including carbon isotope data (Melchin and Holmden, 2006), and conodont biostratigraphic data (Zhang et al., 2006). Additional new graptolite data pertaining specifically to the RhuddanianAeronian boundary interval were reported by Melchin (2013). The following observations were reported by Melchin (2013) and are presented again here.
1) The level of the current GSSP cannot be precisely recognized in the Arctic Canadian succession.
2) A biostratigraphic level corresponding to the base of the D. triangulatus Zone can be recognized based on the succession of closely spaced FADs of Pristiograptus concinnus, D. triangulatus separatus, and Petalolithus sp.
3) The base of the D. triangulatus Zone corresponds closely with the level of a weak (≈ 0.8‰) positive shift in δ13Corg values, which was also observed at Dobs Linn, Scotland (Heath, 1998) at the same biostratigraphic level. Data from Estonia also suggest that a weak positive shift in δ13Ccarb values occurs at or near the base of Aeronian, although the signal is somewhat less clear (e.g. Kaljo and Martma, 2000) and less precisely biostratigraphically defined.
4) The interval in the Cornwallis Island succession that spans the latest Rhuddanianearly Aeronian interval is not marked by any significant biostratigraphic appearance data within conodonts. This is consistent with conodont records in many other parts of the world through this interval.
These data support the observations made in many other parts of the world that the base of the D. triangulatus Zone is a readily recognizable biostratigraphic level in graptolite successions in many parts of the world. Unfortunately, thus far this biostratigraphic level cannot be precisely identified within a conodont or chitinozoan biostratigraphic framework. However, a weak positive shift in δ13C values through this interval, referred to as the Early Aeronian Event by Cramer et al. (2011) and Melchin et al. (2012), may prove to have potential for international correlation, although this remains to be rigorously tested.
The base of the Telychian Stage has been considered to coincide with the base of the Spirograptus guerichi Zone, but recent work in the stratotype area has shown that the level of the GSSP is significantly below the local first appearance of Spirograptus guerichi and that the biostratigraphic succession above the level of the GSSP is more structurally complex than previously suspected (Davies et al., 2013). Thus, the GSSP level cannot be precisely placed within a globally useful biostratigraphic framework.
The presence of a positive δ13C excursion in the upper Aeronian S. sedgwickii Zone was well documented in Arctic Canada by Melchin and Holmden (2006). This succession is relatively condensed and possibly incomplete through the S. sedgwickii Zone (—810 m thickness) and the excursion is represented by a limited number of samples, so the detailed structure of the isotope curve cannot be resolved. In addition, graptolites indicative of the S. sedgwickii Zone are extremely rare in this section, so precise placement of the beginning, the peak, and the end of the excursion interval relative to the graptolite zonal boundaries is not possible. Nevertheless, Melchin and Holmden (2006) showed that the excursion in the S. sedgwickii Zone, referred to as the Late Aeronian Event by Cramer et al. (2011) and Melchin et al. (2012), is likely an event of global significance.
As with the base of the Aeronian, the interval in the Cornwallis Island succession that spans the latest Aeronianearly Telychian interval is not marked by any significant biostratigraphic appearance data within conodonts (Zhang et al., 2006). This is consistent with conodont records in many other parts of the world through this interval.
Melchin et al. (2011) reported the results of detailed sampling of a succession of marine shelf strata in the Arisaig region, NE Nova Scotia, in which the S. sedgwickii Zone is represented by approximately 160 m of strata consisting of black shales, grey shales, bioturbated mudstones and tempestites. A total of 89 samples were analyzed for δ13Corg through this almost continuous succession from the midAeronian, as dated by graptolites, into the lowest Telychian, as determined by brachiopods. Throughout the S. sedgwickii Zone threefour distinct intervals of positive shift of δ13Corg values by 3‰—4.5‰ above midAeronian baseline values (—-30‰) were recognized. The uppermiddle peak is the highest. Each of the peaks is associated with a phase of shallowing within the sedimentary succession. The Arisaig δ13Corg record can be closely compared with a condensed (－2.5 m), but very intensively sampled succession of upper Aeronian black shales, mudstones and siltstones in the Prague Basin, Bohemia, documented by torch and Fryda (2012). This succession also shows threefour distinct δ13Corg positive excursions within the upper Aeronian strata.
These two successions show somewhat different sea level histories and were separated by the Rheic Ocean, suggesting that this three to fourfold pattern of δ13C peaks is not just the result of local effects but is a global or widespread regional signal. In both Nova Scotia and Bohemia the peaks are generally associated with shallowing, which supports the hypothesis that they are related to episodes of glaciation, although the precise causal link between glaciation and positive δ13C excursions remains a matter of debate. The data further suggest that there may have been several glacial cycles through late Aeronian time. In addition, the δ13C record has the potential to provide very highresolution correlation through late Aeronianearliest Telychian interval.
References
Cramer, B.D., Brett, C.E., Melchin, M.J., Mnnik, P., Kleffner, M.A., Mclaughlin, P.I., Loydell, D.K., Munnecke, A., Jeppsson, L., Corradini, C., Brunton, F.R. and Saltzman, M.R. 2011. Revised correlation of Silurian Provincial Series of North America with Global and regional chronostratigraphic units and δ13Ccarb chemostratigraphy. Lethaia, 44, 185202.
Davies, J.R., Waters, R., Molyneux, S.G., Williams, M., Zalasiewicz, J.A., Vandenbroucke, T. and Verniers, J. 2013. A revised sedimentary and biostratigraphical architecture for the Llandovery area, central Wales. Geological Magazine, 15, 300332.
Heath, R.J. 1998. Palaeoceanographic and Faunal Changes in the Early Silurian. Ph.D. Thesis, University of Liverpool, Liverpool, U.K. 239 pp.
Kaljo, D. and Martma, T. 2000. Carbon isotopic composition of Llandovery rocks (East Baltic Silurian) with environmental interpretation. Proceedings of the Estonian Academy of Sciences Geology, 49, 267283.
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Melchin, M.J. 1989. Llandovery graptolite biostratigraphy and paleobiogeography, Cape Phillips Formation, Canadian Arctic Islands. Canadian Journal of Earth Sciences, 26, 17261746.
Melchin, M.J. 2013. A view of the Rhuddanian—Aeronian boundary from Arctic Canada. 217218. In: Lindskog, A. and Mehlqvist, K. (eds), Proceedings of the 3rd IGCP 591 Annual Meeting—Lund, Sweden, 919 June 2013. Lund University.
Melchin, M.J. and Holmden, C. 2006. Carbon isotope chemostratigraphy of the Llandovery in Arctic Canada: Implications for global correlation and sealevel change. GFF, 128, 173180
Melchin, M.J., MacRae, K.D., Frda, J. and torch, P. 2011. A Multiple Carbon Isotope Excursion in the Upper Aeronian S. sedgwickii Zone. In: Loydell, D. (ed.), Siluria Revisited, Ludlow, 2011, International Subcommission on Silurian Stratigraphy Field Meeting, Program with Abstracts.
Melchin, M.J., Sadler, P.M. and Cramer, B.D. 2012. The Silurian Period. In: Gradstein, F.M., Ogg, J.G. and Smith, A.G. (eds), A Geologic Time Scale 2012. Elsevier.
Storch, P. and Fryda, J. 2012. The late Aeronian graptolite sedgewickii Event, associated positive carbon isotope excursion and facies change in the Prague Synform (Barrandian area, Bohemia). Geological Magazine, 149, 10891106.
Zhang Shunxin, Barnes, C.R. and Jowett, D.M.S. 2006. The paradox of the global standard Late OrdovicianEarly Silurian sea level curve: evidence from conodont community analysis from both Canadian Arctic and Appalachian margins. Palaeogeography, Palaeoclimatology, Palaeoecology, 236, 246271.
Global stratotype sections and points and quantitative stratigraphic correlation: A way forward for defining and correlating the Silurian System
Michael J. MELCHIN1, H. David SHEETS2, Charles E. MITCHELL3 and FAN Junxuan4
1Department of Earth Sciences, St. Francis Xavier University, Antigonish, NS, Canada B2G 2W5
2Department of Physics, Canisius College, 2001 Main St., Buffalo, NY 14208, USA
3Department of Geology, University at Buffalo, 876 Natural Science Complex, Buffalo, NY 14260, USA
4State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
The objective of Global Stratotype Sections and Points (GSSPs) is to provide a benchmark for defining each system, series and stage in the geologic time scale. The base of each global chronostratigraphic unit is defined at a particular horizon of a particular locality (the GSSP) and at all other places in the world the base of that unit is recognized by correlation with the GSSP. In practice it is too commonly the case that sections are correlated with GSSPs only on the basis of one or two index taxa whose first appearances occur at the GSSP level, despite that fact that species can be expected to have diachronous first (and last) appearances throughout their geographic range as a result of the ecology and biogeography of species dispersal, as well as the effects of preservation and sampling.
In order to minimize the potential problems of miscorrelation based on only one or a few index taxa, it is recommended that GSSPs should contain “as many specific marker horizons or other attributes favorable for longdistance time correlation as possible” (Murphy and Salvador, 1998), such as other fossil events (preferably including events in two or more different groups of fossil taxa), chemostratigraphic events, and\/or geomagnetic reversals. The best practice is to use the totality of the evidence through the entire continuous section that contains the boundary and correlates with the GSSP level based on the sum of this evidence (Smith et al., 2014).
For the Silurian, an ideal GSSP might be expected to have at least a moderately diverse fauna of graptolites, as well asat least some occurrences of conodonts and\/or chitinozoans, some of the most useful fossil groups for subdivision of Silurian time. On the other hand, an excellent candidate section may have an excellent record of conodonts and chitinozoans, but sparse or absent graptolites. Most sections can also provide a good record of carbon isotopes, either from carbonates, organic matter, or both. The question is how best to simultaneously integrate all of the available fossil and chemostratigraphic data to: a) choose the best candidate section for a new GSSP; b) provide the highest possible resolution in correlation between the GSSP and other sections globally, including sections that represent different facies; and c) evaluate the level of uncertainty or imprecision in those correlations.
Graphic correlation (GC) provides one potential means of simultaneously using all of the available biostratigraphic data, and as well other stratigraphic data such as marker beds and magnetic reversals (e.g. Mann and Lane, 1995), and even isotope curves (e.g. Sadler, 2012). GSSPs have been incorporated into GC composites since the late 1980s (e.g. Sweet, 1984; Kleffner, 1989). A few studies have even used GC as means of testing the relative merits, in terms of correlation potential, of two or more different GSSP candidate sections (e.g. Benoist, 2000; Bettley et al., 2001). Despite the potential value of GC as a tool for testing and evaluating GSSP candidate sections, it has not become widely adopted within GSSP working groups. This may be the result of two potential difficulties with GC. Creation of a GC composite can be a timeconsuming process, particularly if many sections are involved in the creation of the composite. In addition, GC composite solutions are quite sensitive to the process of selection of a starting reference section, the order in which other sections are correlated to the reference, and also the method used for drawing the line of correlation (LOC) (e.g. MacLeod and Sadler, 1995). Ideally, many individual GC solutions could be created from the same data set using difference choices of reference sections, section ordering, and\/or LOC creation method, to evaluate different key sections for their reference potential. Although GC is not amenable to quantitative error analysis, the differences between multiple solutions using the same dataset and a range of alternative choices about starting reference sections and LOC placement could be used to estimate the error or uncertainty in the stratigraphic resolution of the correlations. Unfortunately, this would be a very tedious process.
In order to overcome many of the shortcomings of graphic correlation,several automated correlation methods have been developed that apply the principles of GC to simultaneously correlate multiple sections and create a multivariate line of correlation. Two of those most relevant to the current issues are Constrained Optimization (CONOP, Sadler et al., 2003), and Horizon Annealing (HA, Sheets et al., 2012). The search algorithms used by these methods create a composite ordering of all of the events from all sections in a way that minimizes the misfit (i.e. minimizes total stratigraphic range extensions) between the composite solution and each individual section. Both methods will also allow for the use of other types of geochronological data, such as peaks in isotope curves or magnetic reversals. CONOP and HA differ primarily in that in CONOP, the events that are ordered are first and last appearance events of individual taxa (FADs and LADs) whereas HA orders collection horizons, based on the set of occurrences in each collection. Both methods can produce a composite sequence from a regional or global dataset that can be scaled to geological time.
CONOP and, more recently, HA, have mainly been employed in studies focusing on either refinement of regional and global biochronologies and calibrated geological time scales (e.g. Cooper and Sadler, 2012; Fan et al., 2013) or else studies of biodiversity history and their relationship to paleoecology and paleoenvironmental change (e.g. Sadler et al., 2011; Cooper et al., 2014). CONOP and HA, however, have features that make them well suited to evaluative studies of GSSP candidate sections and also to global correlation of established GSSPs (Smith et al., 2014). For evaluation of GSSP candidate sections and levels, CONOP and HA permit the quantitative rating of the quality of individual sections relative to each other, by measuring the degree of misfit between the data from each section and the composite succession. An individual section with the most complete data set, whose ranges most closely match those of the composite (the least misfit), may be considered favorably as a GSSP candidate. CONOP and HA results also permit comparison of individual taxon ranges between different study sections and also between each section and the composite range chart (see CONOP examples in Sadler et al., 2011). An ideal marker taxon for a GSSP may be considered one that shows relatively consistent patterns in the level of its first appearance between sections. Alternatively, an ideal GSSP level may be one that has a strongly constrained placement in the composite event sequence, within an interval of relatively highly precise correlations among the studied sections.
CONOP and HA also provide means of estimating the precision or confidence with which individual events or levels can be correlated. This can potentially be done in several different ways:1) relaxation of the search criteria in creation of a composite to see how variable the level of an event or sample level appears as criteria are slightly relaxed (e.g. the “relaxed fit curves” produced by CONOP); 2) degree of variation in the level of particular events or sample levels through multiple repeat analyses, with or without slight changes in the data set (i.e. via jackknifing or bootstrapping methods) or search criteria; 3) comparison of the results of analyses by different methods (e.g. CONOP, HA and GC) or by different operational choices within a given method. A sample level or event that shows the least variability in its position of occurrence within composites derived by these different means may be regarded as a good level for a GSSP because its occurrence relative to other events is well constrained by the available data.
In summary, methods of quantitative stratigraphic correlation, particularly CONOP and HA,are able to employ all available stratigraphic data to provide: 1) highresolution correlation between GSSP candidate sections and other sections globally; 2) means of evaluating the potential merits of different GSSP candidate sections and levels; and 3) means of estimating the levels of confidence or precision in the resolution of correlation. We therefore recommend that quantitative stratigraphic correlation (GSC) become part of the process of restudy, selection and correlation of GSSPs for the Silurian System.
References
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